During the next decade, the vastly increased amount of information that will be generated by advanced sensors and computing systems must be captured and stored by a new generation of high data rate, high capacity recording and buffering systems that provide rapid, reliable access to the stored data. As an example, the Space Telescope is expected to generate a terabyte (10.sup.12 bytes) of data per year during its 15-year planned life. A computer compatible magnetic tape archiving system for this amount of data would consist of approximately 100,000 tapes at 150 megabytes per tape. As a more dramatic example, the Space Station to be launched in the early 1990's is expected to generate a terabyte of data per day at data rates that can exceed a gigabit (10.sup.9 bits) per second. For the same reasons that the archival storage technology will be severly strained to meet the challenge of storing this veritable flood of information, so also will the data buffering technology, in its attempt to provide equipment which will receive, temporarily store, access, and transfer vast quantities of data on a real time basis.
High density optical recording systems which may be used for recording and playing back information are known in the prior art. For example, U.S. Pat. No. 4,097,895, entitled "MULTI-LAYER OPTICAL RECORD," issued on June 27, 1978, to F. W. Spong, relates to an optical disk record/playback system herein data are recorded on the surface of a recording medium. In a Spong system the thermal energy of a focused high intensity light beam causes variations in the optical properties on the surface of the recording medium. For example, in one system the thermal effects of a laser beam form pits in an absorptive coating on the surface of an optical disk. In the Spong system, approximately 10.sup.11 bits of information can be recorded on one side of a disk-shaped record medium having a thirty centimeter diameter.
Although the system of the previous example is directed toward archival, or permanent, storage, there have developed in recent years erasable media and recording techniques. Currently, magneto-optic materials are used in the state-of-the-art recording media to effect readily alterable recordings. A magneto-optic recording medium is a magnetic material which causes the polarization angle of laser light to be changed when reflected from a recorded spot. In preparation for recording or playback operation, the molecules of the magneto-optic material across the entire recording surface are vertically oriented in one direction. During recording, the molecules of the magneto-optic material at the point of incidence of a laser beam are flipped in the opposite direction due to the presence of a magnetic field of a given strength and polarity and the heating induced by the laser. Illumination from a playback laser beam of lower power reflected from this area will show a polarization angle change. The erasing technique then is to restore the molecular orientation condition which existed prior to recording and/or playback with a magnetic field and continuous wave laser beam present.
Information recording and retrieval systems are also known where the rate at which information is recorded or played back may be increased by two, three or more times over a Spong type system by recording or playing back multiple tracks of information simultaneously. In U.S. Pat. No. 4,449,212, issued May 15, 1984, to C. W. Reno, the output of a single gas laser is split into multiple beams which, for purposes of recording, are independently modulated and used to simultaneously record data at extremely high rates on the surface of an optical disk. In the playback mode, the Reno apparatus splits the laser output beam into multiple, constant intensity, low power beams for illuminating the recorded tracks.
At the present time, the apparent practical upper limit of the data rate of a Spong type system is in the order of 25 megabits per second. Adding multi-track capability, as in the Reno patent, of, for example, nine data tracks, still achieves less than one-quarter gigabit per second operation. In order to record incoming data and playback previously stored data at the one gigabit per second rate mentioned earlier, an information buffering system must be capable of providing data rates in excess of one gigabit per second, in order to account for the overhead of information processing.
U.S. patent application, Ser. No. 803,003 filed Nov. 29, 1985, for M. L. Levine et al., and assigned to the same assignee as the present invention, discloses a multi-disk optical information system which includes twelve disks each having two erasable recording surfaces. Independently controllable optical platforms, driven by linear motors, move the twenty-four optical heads radially across the disks so as to follow preformatted pilot tracks permanently scribed on the disk surfaces. Each optical head can record/playback eight simultaneous data tracks, so that the system can potentially provide 192 data channels. The erasable recording medium on the disk surfaces is a magneto-optic substance with the result that the disks may be reused an unlimited number of times.
The key structural component of the Levene et al. optical information system is the multidisk spindle, a rotating shaft to which the optical disks are mounted. The disks of this system are typically fourteen inches in diameter. It is of utmost importance that the disks be positioned and aligned on the shaft such that all disks rotate in parallel with each other and perpendicular to the centerline of the shaft. Furthermore, during assembly, the disks must be axially positionable such that the performatted disk tracks are concentric with the axis of rotation of the spindle, typically the shaft centerline.